The field of art to which this invention pertains is the purification of a diolefin hydrocarbon stream containing trace quantities of acetylene compounds. The production of diolefins is well known and widely practiced to produce a wide variety of products and precursor products utilizing a variety of diolefin production processes including naphtha cracking processes and by-products from fluid catalytic cracking processes. Most of these diolefin production processes produce undesirable trace quantities of acetylene. One technique which is used to purify diolefin streams selectively hydrogenates the acetylene while minimizing the destruction or hydrogenation of the diolefin compounds.
The selective hydrogenation of the acetylene compounds is generally conducted in the presence of a selective hydrogenation catalyst and hydrogen and conducted at an elevated pressure and temperature. Such selective hydrogenation catalysts are well known in the art and include, for example, a catalyst containing copper metal associated with one or more activator metals impregnated on an alumina support. During the acetylene hydrogenation polymers are formed and deposited on the catalyst thereby reducing the activity of the catalyst. One known method of regenerating spent or partially spent catalyst is to perform a controlled carbon burn and subsequent metal reduction to remove catalyst contaminants which are formed as an undesirable by-product of the acetylene hydrogenation. The carbon burn regeneration techniques necessarily require that the reaction zone containing the spent catalyst be taken off-line and that ancillary regeneration equipment be provided.
U.S. Pat. No. 3,634,536 B1 (Frevel et al) discloses a process for selectively hydrogenating acetylenic impurities in an isopropene- or butadiene-containing stream whereby carbon monoxide is utilized during hydrogenation over a copper-based catalyst.
U.S. Pat. No. 4,440,956 B1 (Couvillion) discloses a catalyst for the removal of acetylenes from liquid hydrocarbon streams with a minimum loss of diolefinic unsaturation present in the liquid composition.
U.S. application Ser. No. 09/358,795 filed on Jul. 22, 1999 discloses a process for an on-line regeneration of a selective hydrogenation catalyst with a solvent.
U.S. application Ser. No. 09/359,629 filed on Jul. 22, 1999 discloses a process for an off-line regeneration of a selective hydrogenation catalyst with a solvent.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial activities, there is always a demand for new selective hydrotreating processes which provide lower costs, higher selectivity and longer on-stream operation.
The present invention maintains the high activity of the selective hydrogenation catalyst during an extended run length. Higher average product quality when integrated over time on-stream improves the process economics and demonstrates the unexpected advantages. In addition, the quantity of make-up regeneration solvent is significantly reduced.
The present invention is a selective acetylene hydrogenation process which is able to produce a high quality diolefin having extremely low levels of acetylene over an extended period of time compared with the prior art. The process of the present invention provides a selective hydrogenation reaction zone wherein the catalyst activity is maintained at a high level while the process unit remains on stream by contacting the selective hydrogenation catalyst with a polymer solvent, diolefin feed and hydrogen in one embodiment and by contacting the selective hydrogenation catalyst off-line with only polymer solvent and hydrogen in a second embodiment.
In accordance with one embodiment, the present invention relates to a process for the purification of a diolefin hydrocarbon feed stream containing trace quantities of acetylene compounds which process comprises: (a) contacting the diolefin hydrocarbon feed stream containing trace quantities of acetylene compounds and hydrogen with a selective hydrogenation catalyst in a selective hydrogenation zone to selectively hydrogenate at least a portion of the acetylene compounds; (b) contacting the resulting selective hydrogenation catalyst containing polymer compounds produced in step (a) with a polymer solvent and hydrogen to produce a stream comprising polymer solvent and dissolved polymer compounds;, (c) separating the stream comprising polymer solvent and dissolved polymer compounds to produce a stream comprising polymer solvent and having a reduced concentration of polymer compounds, and a stream rich in polymer compounds; (d) recycling at least a portion of the stream comprising polymer solvent and having a reduced concentration of polymer compounds to step (b) to supply at least a portion of the polymer solvent; (e) recovering the stream rich in polymer compounds produced in step (c); and (f) recovering a diolefin hydrocarbon stream having a reduced concentration of acetylene compounds produced in step (a).
In accordance with another embodiment, the present invention relates to a process for the purification of a diolefin hydrocarbon feed stream containing trace quantities of acetylene compounds which process comprises: (a) contacting the diolefin hydrocarbon feed stream containing trace quantities of acetylene compounds with a polymer solvent and introducing: the resulting admixture together with elemental hydrogen into a selective hydrogenation zone containing a selective hydrogenation catalyst to selectively hydrogenate at least a portion of the acetylene compounds; (b) passing the resulting effluent from the selective hydrogenation zone in step (a) to a first fractionation zone to produce a diolefin hydrocarbon stream having a reduced concentration of acetylene compounds and a stream containing polymer solvent and polymer compounds; (c) recycling at least a portion of the stream containing polymer solvent and polymer compounds to provide at least a portion of the polymer solvent in step (a); (d) passing at least another portion of the stream containing polymer solvent and polymer-compounds to a second fractionation zone to produce a stream containing polymer solvent and having a reduced concentration of polymer compounds, and a stream containing polymer solvent and having an increased concentration of polymer compounds; (e) recovering the stream containing polymer solvent and having an increased concentration of polymer compounds; and (f) recovering the diolefin hydrocarbon stream having a reduced concentration of acetylene compounds produced in step (b).
In yet another embodiment, the present invention relates to a process for the purification of a butadiene hydrocarbon feed stream containing trace quantities of acetylene compounds which process comprises: (a) contacting the butadiene hydrocarbon feed stream containing trace quantities of acetylene compounds and hydrogen with a selective hydrogenation catalyst in a selective hydrogenation zone to selectively hydrogenate at least a portion of the acetylene compounds; (b) contacting the resulting selective hydrogenation catalyst containing polymer compounds produced in step (a) with a polymer solvent comprising an alkane having from 4 to about 8 carbon atoms and hydrogen to produce a stream comprising polymer solvent and dissolved polymer compounds; (c) separating the stream comprising polymer solvent and dissolved polymer compounds to produce a stream comprising polymer solvent and having a reduced concentration of polymer compounds, and a stream rich in polymer compounds; (d) recycling at least a portion of the stream comprising polymer solvent and having a reduced concentration of polymer compounds to step (b) to supply at least a portion of the polymer solvent; (e) recovering the stream rich in polymer compounds produced in step (c); and (f) recovering a butadiene hydrocarbon stream having a reduced concentration of acetylene compounds produced in step (a).